Comments
on the Cawthra Old Growth Forestby
Paul F. Maycock, Forest Ecologist,Erindale
College, University of Toronto.

June, 17, 1998

In early summer
1959 while conducting a survey of the Deciduous Forests of extreme Southern
Ontario (Maycock, 1963), I came across an extensive area of forest at the
Dixie interchange on the Queen Elizabeth Highway. Much later I was to learn
that this had long been known as the Cawthra Forest. Later, in 1969, I
moved from McGill University to Erindale College of the University of Toronto,
and came into contact with a number of biologists and naturalists who were
keenly interested in this forest complex and some were involved with ecological
assessment research for the Ministry of Natural Resources who was searching
for candidate nature reserves. Throughout the province, Cawthra Forest
was highly rated and so it should have been because of its many unusual
features. At the time I thought how fortunate for the City of Mississauga
that it had such an interesting large area of old growth natural forest
which is so useful for education, nature conservation and for nature appreciation
and the recreation of its citizens.

This stand
of deciduous forest was quite extensive and variable and I selected a higher
better drained mesic section and quantitatively sampled it for its composition
in 1959. It contained a total of 16 different tree species, 13 in the upper
canopy and 3 in the lower. Of these Sugar Maple (Acer saccharum)
was the most important with an importance value of 119 of a possible 300
for the stand. The second species was White ash (Fraxinus americana)
with importance of 50, followed by Black Cherry (Prunus serotina),
importance 43, and Basswood (Tilia americana) importance 24 and
White Elm (Ulmus americana) with importance also of 24, the latter
forming about 14% of the standing trees. Other tree species with their
importance included Pin Cherry (Prunus pensylvanica) (8), Paper
Birch (Betula papyrifera) (8), Large toothed Aspen (Populus grandidenta)
(7), Red Maple (Acer rubrum) (6), Silver Maple (Acer saccharinum)
(5), Red Oak (Quercus rubra) (3), Yellow Birch (Betula lutea)
(2), Serviceberry (Amelanchier arborea) (2), Beech (Fagus grandifolia)
(1), Hop Hombeam (Ostrya virginiana) (1), and Chokecherry (Prunus-virginiana)
(1). On the basis of these quantitative contributions to the composition
of the forest we can describe it as a Sugar Maple119 - White
Ash50 - Black Cherry43 forest type.

Two comments
should be made about the tree composition. Although not too important,
some species indicated past disturbance and successional development, including
Large-tooth Aspen, Pin Cherry and Paper Birch. The complement of trees
did not include any considered to be strongly Carolinian, although this
cannot be considered in any way criminal or neglectful, because the site
is influenced by colder than normal microclimate and it and the surroundings
were seasonally quite wet. As well, many of the dominants in the Cawthra
forest are also dominant or important in stands with a component of Carolinian
trees. From a successional or developmental aspect, the forest is gradually
trending toward a terminal or climax situation for this region. Most of
the reproduction is Sugar Maple (163 of a total value of 200) and Beech
is also entering the stand.

The understorey
was quite striking in that it was heavily populated by a great variety
of tree seedlings, shrubs and herbs, actually a total of 75 were recorded.
These populations vary seasonally as in all deciduous forests but major
members contributing to biomass included Allium tricoccum) (Wild
Onion), Erythronium americanum (Dog-tooth Violet), Maianthemum
canadense (Wild Lily-of-the-Valley), Hepatica acutiloba (Hepatica),
Osmorhiza claytoni (Wild Licorice), Smilacina racemosa (False
Solomon's Seal), Trillium grandiflora (White Trillium), Viola
pensylvanica (Yellow Violet), and Arisaema atrorubens (Jack-in-the-pulpit).
There was great variety and some groups were represented by a number of
species - 5 ferns, 3 different violets, and fully 8 different species of
Carex (Sedge) - C. albursina, C. gracillima, C.
intumescens, C. pedunculata, C. rosea, C. plantaginea,
C. communis and C. leptonervia.

Although Carolinian
trees were not well represented, many understorey plants are in this group
- Cryptotaenia canadensis (Honewort), Carex albursina (Wide
Sedge), Dicentra canadensis (Squirrel Corn), Hamamelis virginiana
(Witch Hazel), Leersia virginica (Cutgrass), Menispermum canadense
(Moonseed Vine), Viburnum acerifolium (Maple-leaved Viburnium) and
Viola canadensis (Canada Violet), to name a few. Interestingly,
there is also a component of northern species which are uncommon southward,
but which are found in the Cawthra forest. These are Prunus pensylvanica
(Pin Cherry), Clintonia borealis (Blue-bead Lily), Viola pallens
(White Violet) and Streptopus roseus (Rose Mandarin). It would seem
that Cawthra has the best of both forest worlds in Ontario - north and
south.

At a time when
the scientific community is strongly involved with the phenomenon of diversity,
the species richness found at Cawthra is striking, not only in terms of
numbers, but also in variety.

The writer
has been working in mesic old growth deciduous forests throughout the North
Temperate Region and has quantitatively sampled them in Japan, China, Ukraine,
Poland, Slovakia, Czech Republic, Yugoslavia, England, eastern United States,
as well as Canada. He is presenting a paper on the biodiversity of these
forests in Florence, Italy in July at the Seventh International Congress
of Ecology. Having assembled a body of quantitative data on these forests,
I was interested to see how the Cawthra Forest compared. The highest species
number in any of my stands was 127 and the lowest only 17. Cawthra stood
50th in a total of 60 stands with 92 species. Thus plant diversity
is quite high here and with the finds for salamanders and other organisms,
it is probably true for most biological phenomena. I was quite surprised
at this result because comparatively Cawthra is quite north latitudinally
in comparison to many of the other stands.

The structural
features, the compositional aspects, the environmental and ecological characteristics
emphasize the old growth deciduous forest nature of the Cawthra Forest.
It is a unique ecological entity, the like of which is rapidly disappearing
in Southern Ontario. It has intrinsic value for study, for research, for
a benchmark to record environmental and other ecological changes, a diverse
haven for birds, animals, plants and other living organisms, and above
all a place of natural wonder. Old growth systems are being set aside and
protected throughout the world because of their tremendous ecological versatility.
When limited public access is made available, the public is enthralled
by them and more so the older they become.

If the activities
of managers in the city of Mississauga within Cawthra Forest in the past
10 years are examined, it seems they are quite unappreciative of its natural
values - a sewer corridor, the introduction of foreign plantings with the
thought of increasing diversity, it will do the opposite - destroy natural
diversity and increase that of weed species. It would seem they are attempting
to create a park of it. A park can be created almost anywhere and on any
site. There is just one opportunity to set up an old growth system and
establish a set of regulations to perpetuate it. If the opportunity is
let slip past, it is gone forever. There are parks throughout Mississauga.
How many old growth forests are there?